Luteinizing follicular cyst in a dog
History: Tissue from an 11 month old female Great Dane. The tissue was removed during a routine spay surgery and submitted for histopath due to abnormal appearance.
Ovary: In each section examined there are primary follicles present in a fibrovascular stroma. There are two normal corpora lutea present consisting of a large solid mass ofpolygonal cells with large intracytoplasmic lipid vacuoles (luteinized cells). In addition there are two large cystic follicles partially lined by luteinized cells and partially lined by follicular epithelium.
Luteinized ovarian cysts are derived from anovulatory Graffian follicles. They are differentiated from cystic corpora lutea by the absence of a break in the wall of the cyst where ovulation has occurred. They are uncommon in dogs and the clinical significance is usually negligible. They can occur in clinically normal dogs, and be seen in dogs with pyometra and cystic endometrial hyperplasia. CEH and pyometra often occurs in the absence of such cysts, and generally happens through persistent hormonal stimulation of the corpora lutea which can persist following ovulation.
Bacterial infection or foreign material within the uterus may cause CEH and pyometra during the luteal phase of the cycle. Excess estrogenic stimulation can also lead to CEH-pyometra. Progesterone is the major hornome stimulating CEH and pyometra in the dog; but the endometrium responds best to progesterone following priming by estrogen.